switch_false currently returns false on NULL
FS-6286 --resolve Thanks to Tom Parrott
FS-5755

rtp_secure_media=mandatory
rtp_secure_media=optional
rtp_secure_media=mandatory:AES_CM_256_HMAC_SHA1_80,AES_CM_256_HMAC_SHA1_32
rtp_secure_media=optional:AES_CM_256_HMAC_SHA1_80
rtp_secure_media=forbidden

true implies mandatory
false implies forbidden
not set implies optional

rtp_secure_media_inbound or rtp_secure_media_outbound take precedence and are treated the same way based on leg direction
remove unused stuff from last commit
Documentation for recent SRTP changes
default if not set is
spacing
add optional rtp_secure_media_suites variable clobbered by rtp_secure_media with mandatory|optional:<suites>
THIS JUST IN rtp_secure_media_suites option
Spacing
React to all suites in the defaults and set true to accept the strongest offer received
Fix minor edge case in switch_split_user_domain

If the input started with 'sip:sips:' it would have been incorrectly
parsed.